Categories
Cold War US Heavy Prototypes

120mm Gun Tank T43

U.S.A. (1951)
Heavy Tank – 6 Prototypes Built

On September 7th, 1945, military heads of the Western Powers were horrified by what they saw rumbling towards them along Charlottenburger Chaussee in central Berlin during the Victory Parade. Celebrating the end of the Second World War, the increasingly threatening Soviet Union unveiled its latest tank to the world: the IS-3 heavy tank. As these machines clattered down the parade route, a sense of consternation enveloped the representatives of the British, US, and French armies. What they saw was a tank with well-sloped and apparently heavy armor, a piked nose, wide tracks, and a gun at least 120 mm in caliber, and belonging to a future potential adversary. The IS-3 was clearly a serious potential threat to their own tank forces in any such conflict.

The race was on. France, Britain, and the US immediately began to design and develop their own heavy or heavily armed tanks. The British would eventually create the Conqueror Heavy Gun Tank, while the French experimented with the AMX-50. Both of these tanks had 120 mm guns that would, in theory, be able to combat the IS-3 threat. Two branches of the US Armed Forces would support the creation of a new American heavy tank. These branches were the US Army and the Marine Corps. Realising that the heavy tanks conceived during WW2, such as the T29, T30, and T34, were unfeasible, both branches set out to develop a new heavy tank that would eventually be known as the 120 mm Gun Tank M103.

Although the need for a heavy tank was urgent to fight the perceived IS-3 threat, it would take until 1948 before the development of the T43 heavy tank would actually start because of various issues, including budget and disarmament. Both the Marine Corps and Army were interested in the future heavy tank, but when various forces within the US Army started opposing the T43, it was the Marine Corps that would eventually give the leverage needed for full production. The first 6 of these vehicles were pilot vehicles which would lay the foundations for the M103 heavy tank, the only heavy tank to be used in active service of the United States.

The T43 Pilot #1, Aberdeen Proving Ground July 7 1951.
Source: Firepower, Hunnicutt

Genesis

The T43 (M103) was a project of the US Army with the goal of developing a heavy tank capable of defeating enemy heavy tanks at combat ranges and deliver heavy fire-support for both infantrymen and medium tank battalions in offensive and defensive roles. It was to be superior to the previously developed T34 heavy tank, specifically in mobility, flexibility, and component availability. The USMC had an interest in the project because of their amphibious warfare doctrine. Initially, the Army would be the lead branch supporting the development of the M103 (then known as T43), but as development dragged on, the Army would lose interest. The Marine Corps would be the driving force behind the upgrade programs to fix some of the larger mistakes the tank had, which the Army did not do. Although the goals of the two branches were mostly the same, their reasons and experiences that led to the development of the T43 and its eventual service as the M103 were quite different.

The Army

Brigadier General Gladeon M. Barnes
Source: United States Army

The story of the Army part of the development begins in 1944 with Brigadier General Gladeon M. Barnes. Barnes was the head of the US Army’s Ordnance Technical Division (OTD) during the Second World War. In short, he was the head of development and acquisition of weapon systems for the US Army, including tanks and armored vehicles. Throughout the war, he had advocated for heavier tanks and tank guns, but had met stiff opposition from Army Ground Forces (AGF) under Lesley McNair.

When the Allies had to face off against the Tiger II and increasing numbers of Panthers in 1944, of which the latter was originally perceived as a heavy tank instead of a Panzer IV replacement, Barnes would receive much less opposition against his heavy tank programs. Those projects took form as the T29 and T30 heavy tanks and would eventually serve as testbeds for many components used in later US tanks. The AGF objected to the T30’s heavy ammunition and requested for the rearmament of the T29 platform, designated T34, which was to be armed with a converted 120 mm anti-air cannon. The T29, T30, and especially the T34, with its 120 mm gun, would pave the way for the M103.

T34 Heavy Tank
Source: War Thunder Forum

With the end of WW2, the development and production of the aforementioned heavy tanks would come to a halt, as there was no need for them anymore. But then, on September 7th, 1945, the need for a heavy tank would be renewed as the last armored column of the 1945 military victory parade in Berlin drove past the military heads of the Western powers. A new challenger had made its way on the stage: the IS-3 had arrived.

As early as January 1945, the Army had started conducting an equipment requirements study for a post-war situation. In June 1945, this study would be finished and recommended the adoption of a new generation of light (25 US tons / 22.7 tonnes), medium (45 US tons / 40.8 tonnes) and heavy tanks (75 US tons / 68 tonnes), and a prototype 150 US ton (136 tonnes) super-heavy tank. It also gave the following specifications of the recommended heavy tank: a five-man crew, a sustained maximum speed of 20 miles per hour (32 km/h) on a 7-degree slope, fording ability of at least equal to the tank’s height, interestingly, a main gun not larger than 90 mm capable of penetrating 10 inches (254 mm) of armor at a 30-degree vertical slope from a distance of 2,000 yards (1,830 m) with special ammunition, accurate fire at a range of 4,000 yards (3,660 m) with a dispersion limit of 0.3 mils (a dispersion of 1.08 inch per 100 yards or 3 cm per 100 meters) and the frontal hull and turret should have an effective armor of 10.5 inches (267 mm). In January 1946, the Army declared its entire tank force, with the exception of the M4A3E8(76)W Shermans and M26 Pershing, obsolete (the Pershing was later reclassified as a medium tank in May 1946).

During the same month, another requirements study, done by the Department of War, was finished. This requirements study also recommended the adoption of new light, medium and heavy tanks which would eventually receive the designations T41, T42, and T43 respectively, while dropping the super-heavy tank and laying emphasis on developing components to be used specifically for tanks.

The Marine Corps

Major General Oliver P. Smith (left) and Lieutenant Colonel Arthur J. Stuart (Right)
Sources: M103 Heavy Tank, Kenneth Estes and USMC

The story of the Marine Corps part of this development begins in September 1944 at the beaches of Peleliu. There, the Marines landed with armored support, consisting of 30 Sherman tanks. They were met by well dug-in enemy forces, artillery, and mortar fire. The Japanese responded to the invasion by launching a counter-attack with 17 tanks supported by infantry. The Marines were caught by surprise and the Shermans still had to get into position. The light Japanese vehicles were destroyed by bazookas, Shermans, and various other anti-tank weapons during the counter-attack.

Two key players, who were going to have a profound influence on the acquisition of a heavy tank for the Marine Corps and were essential to the development of the M103, bore witness to the Japanese tank-infantry counter-attack. These were Lieutenant Colonel Arthur J. Stuart, who commanded the 1st Tank Battalion at Peleliu, and Major General Oliver P. Smith, who was a ground commander during the battle. These men ensured that the Marine Corps got its heavy tank, with Lt. Col. Stuart being one of the most important advocates of integrating tanks in Marine Corps doctrine during the early post-war situation.

On March 22nd, 1946, now Brigadier General and Commandant of the Marine Corps Schools, Oliver P. Smith wrote to the Commandant of the Marine Corps Alexander A. Vandegrift the following:

‘’In general, the tanks with which the Marine Divisions ended the war are now definitely obsolete. The tank for the future must be capable of withstanding greater punishment, be more mobile, and have improved hitting power. The present tanks are too slow and too vulnerable to anti-tank weapons.’’

This conclusion was based upon the experience of Lt. Col. Stuart who remarked:

‘’Had the Japanese possessed modern tanks instead of tankettes and had they attacked in greater numbers the situation would have been critical.’’

General Alexander Vandegrift responded by purchasing M26 Pershings as substitute heavy tanks and waiting until the Army developed new tanks that the Marine Corps could adopt. Whereas the Marines fought Japanese light tanks during the War in the Pacific, they potentially had to face significantly more powerful and more heavily armored Soviet medium and heavy tanks during the Cold War.

M26 Pershing in Korea.

The reason for the Marines desire for a heavy tank came from their doctrine of amphibious warfare, developed in 1935, which had called for the deployment of tanks during a beach assault. This doctrine consisted of 2 phases of amphibious assault, of which the first phase, the initial landing phase, was to be supported by a light landing tank for infantry support and clearing beach defenses. The second phase was to be supported by a medium tank to carry the battle inland, destroy heavier positions and repel any armored counter-attack. During WW2, the first phase was to be carried out by the M3 Stuart and the second phase by the M4 Sherman. The Stuarts proved to be ineffective at Tarawa in late 1943 and their role was taken over by the M4 Sherman, now carrying out both the first and second phase of the assault. Naturally, the second phase should now be carried out by heavy tank battalions in the post-war scenario.

The T34 needs to lose weight

Although the need for more capable tanks for the post-war situation was clear, the actual start of developing the T43 began as late as 1948. The lack of budget and direction caused the Army to invest in developing components instead of tanks. By testing components used in existing tanks, such as the T29 and T34, the Army developed a whole range of tested components that could be combined into a new tank. Components like the Continental AV-1790 engine and CD-850 transmission can be found throughout the Patton series and the M103 as well. This development approach, although the best solution for the US Army’s low budget long-term tank development, would plague the future tanks with underpowered engines and rushed development.

Development of the T43 began with the rejection of the most promising heavy tank prototype the Americans had at the time, the T34. The 70-US ton (54.4 tonnes) heavy tank was rejected because of its weight, which led to poor mobility and maneuverability characteristics, which could not meet the post-war requirements of both the Army and the Marine Corps. The rejection of the T34, combined with a deteriorating world situation, caused the Army to start undertaking the development of the later designated T41, T42, and T43 tanks that were recommended by the equipment requirements study in May 1946. Although the Army faced severe budget cuts after World War 2, caused by extreme demobilization, public pressure, servicemen pressure for demobilization, and the debate if nuclear weapons would replace conventional armies, the Army still decided to develop its heavy tank.

Multiple conferences were held at the Detroit Tank Arsenal in 1948 to establish the specifications of the new heavy tank. Using previously developed vehicles, such as the T34, these conferences combined with studies from the Detroit Tank Arsenal estimated that a lighter heavy tank could be made by shortening the T34’s hull, using highly angled armor, and arming it with a lighter version of the 120 mm T53 gun that was used on the T34. This modified design would weigh 58 US tons (52 tonnes) and met firepower, protection, and mobility requirements.

The characteristics of the now designated T43 were specified as a feasible design in December 1948. The tank kept the 80 inch (2,032 mm) diameter turret ring, the crew was reduced from 6 to 4 members by eliminating the assistant driver and one of the two loaders. By eliminating one of the loaders, the need for an ammunition handling system was identified. The tank was to have 7 road wheels, compared to 8 road wheels on the T34, with a ground pressure of 11.6 psi (80 kPa) and 28 inch (711 mm) wide tracks. The 12-cylinder gasoline Continental AV-1790-5c engine with a gross 810 horsepower (Net 690 hp) was selected in combination with the CD-850 transmission. A supercharged version of the AV-1790 was considered, which would have delivered a gross 1,040 horsepower, but this would have required the design of a new and untested transmission. A lighter version of the 120 mm T53, along with a .50 caliber coaxial machine gun, were to be installed in the combination gun mount T140. The design also called for two .30 caliber remote-controlled machine guns mounted in blisters on the turret side along with a .50 machine gun for anti-air purposes. The main gun was to be elevated and traversed by an electric-hydraulic system. A range finder, direct sight telescope, lead computer, and panoramic telescope were to be used for the fire control system. The T43 presented 5 inches (127 mm) of the frontal hull and turret armor.

The early design concept of the T43 Heavy Tank. Note the remote-controlled blister machine guns at the back of the turret.

Arming the T43

The previously mentioned conferences held at the Detroit Tank Arsenal in 1948 decided in December that the T43 heavy tank was to be armed with a lighter version of the 120 mm T53 which was used on the T34 heavy tank. The 120 mm T53 gun came into existence after the Ordnance Department undertook design studies in early 1945 to modify the 120 mm M1 anti-aircraft gun to serve as a tank gun. These studies determined that the 120 mm T53 would achieve greater anti-tank performance than the 105 mm T5E1 and the 155 mm T7 which were used on the T29 and the T30.

The 120 mm T53 was a rifled gun, 60 calibers in length (7.16 m), and weighed approximately 7,405 pounds (3,360 kg). It used two-piece ammunition, like the anti-aircraft gun it was derived from, and could handle a maximum pressure of 38,000 psi (26.2 x 10^4 kPa). The gun could fire an estimated 5 rounds per minute and was loaded by two loaders. Its Armor Piercing (AP) round was estimated to be able to defeat 7.8 inches of armor at 1,000 yards and 30 degrees (198 mm at 910 m). Its High Velocity Armor Piercing (HVAP) round was estimated to be able to defeat 11 inches of armor at 1,000 yards and 30 degrees (279 mm at 910 m).

The new guns that were proposed for the T43 were the T122 and T123 120 mm guns. These guns also used two-piece ammunition and were both 60 calibers in length as well (7.16 m). The T122 was virtually the same gun as the 120 mm T53 but weighed approximately 6,320 pounds (2,867 kg), 1,085 pounds (492 kg) lighter than the T53. The T123 was a more powerful gun than its T53 and T122 counterparts.

The T123 was made with cold working techniques. This meant that the gun was made at temperatures below the point that would change the structure of the steel. The advantage of using cold working techniques instead of hot working techniques, which was used for the T53 and T122, is that the material becomes harder, stiffer, and stronger. By using cold working techniques, the T123 gun was both lighter and more powerful than the T122. The T123 weighed approximately 6,280 pounds (2.849 kg) and could handle a maximum pressure of 48,000 psi instead of 38,000 psi (331 mPa instead of 262 mPa). The increase in pressure effectively meant that the US army could fire the gun with more propellant and thus increase the gun’s muzzle velocity and penetration.

During the October 1949 Detroit Arsenal Conference, the following estimated details about the proposed guns and ammunition types were presented:

Characteristics

T122

T123

Projectile

APC

HVAP

APDS

APC

HVAP

APDS

Muzzle velocity

3,100 fps
945 m/s
3,550 fps
1,082 m/s
3,300 fps
1,005 m/s
3,300 fps
1,005 m/s
4,000 fps
1,219 m/s
4,200 fps
1,280 m/s

Penetration, 1,000 yards 30 degrees (914 m)

8.4 inch
213.4 mm
10.9 inch
276.9 mm
14.5 inch
368.3 mm
9.2 inch
233.7 mm
12 inch
304.8 mm
13.6 inch
345.4 mm

Penetration, 2,000 yards 30 degrees (1829 m)

7.6 inch
193 mm
8.8 inch
223.5 mm
13.6 inch
345.4 mm
8.3 inch
210.8 mm
10.2 inch
259.1 mm
12.3 inch
312.4 mm
Ammunition table as presented during the October 1949 Detroit Conference
Source: Kenneth Estes, http://www.tank-net.com/forums/index.php?showtopic=9553&page=5

A gun-versus-armor test for Army Field Forces representatives was reported on December 19th, 1949, carried out at Aberdeen Proving Ground. In this test, various guns were selected to try and penetrate a 5 inch (127 mm) plate of armor at 55 degrees, representing the upper hull armor of the IS-3. The 120 mm T53, the gun on which the T122 was based, failed to penetrate the armor.

On February 16th, 1950, Ordnance obtained approval for the development of the T122 and the T123 guns.

Development of 120 mm ammunition, which had been going on since the end of WW2, placed much emphasis on HVAP and HVAP-DS (High Velocity Armor Piercing Discarding Sabot) rounds. These rounds needed valuable resources, such as tungsten, and caused very high bore erosion which significantly lessened the gun tube life. The advantage was that these rounds were subcaliber rounds, which resulted in high muzzle velocities and flat trajectories to the target. Various studies were conducted which concluded that the HVAP rounds showed no better results than a full caliber APC round. Because the T123 fired its ammunition at a higher muzzle velocity, it was an economic solution, as its APC round performed better than the APC round of the T122 and performed sufficiently enough for it to be used instead of the T122’s HVAP round. In a way, the T122 was seen as an interim gun until the development of the T123’s ammunition was completed.

Additionally, new advances made the development of 120 mm HEAT ammunition viable for the T43. The development of the T153 HEAT ammunition began on September 1st, 1950. These rounds presented high muzzle velocities without losing penetration over distance or impact. The T153 was initially estimated to penetrate 13 inches of armor (330 mm), but later reached 15 inches (381 mm) of armor penetration at all ranges. The HEAT round had a muzzle velocity of 3,750 fps (1,143 m/s), which made it theoretically more accurate than the APC round, which had a lower muzzle velocity.

The T123 was initially mounted in the same T140 gun mount as the T122 gun, but further studies resulted in the design of a more conventional and reliable gun mount for the T43 which was implemented into all production tanks. This redesigned gun mount received the designation combination gun mount T154 and is first mentioned in an OCM of July 10th, 1951. The redesigned gun mount resulted in a redesign of the T123 gun, which was now known as the T123E1 and featured a quick change gun tube.

Various ammunition types were developed for the T53, T122, and T123 guns. The T14E3 APC round was developed for the T43 and T122 guns, while the T99 APC round was developed for the T123. An AP round was developed for both the T122 and T123 guns as well, designated the T116 (for the T122) and T117 (for the T123), respectively. Additional ammunition types that were in development guns were the T102 HVAP-DS, T153 HEAT, T143 HEP, T15 HE, T147 Target Practice, T16 Smoke, and T272 Canister rounds.

Projectiles and propellant for the T123 120 mm gun.

Development on the T123 proceeded so quickly and satisfactorily, that the development of the T53 and T122 guns was canceled on either February 6th, 1952, April 10th, 1952, or May 1952, depending on sources.

The T123E1 was selected as the main gun of the production vehicles. The development of various ammo types for the T123 gun was eventually canceled. In June 1953, the T117 AP and the T99 were canceled after the promising T116 APC shell was developed. Eventually, three types of ammunition were required for service: APC, HEAT, and HE, although smoke and a target practice round were developed and used as well.

The 120mm T123E1 gun, the main armament of the T43.
Source: Tankograd T-10

How many T43’s do we need anyway?

The new heavy tank faced some initial criticism from a British liaison officer, who identified that the vehicle did not comply with expected agreements of the upcoming Tripartite Tank Conference between Canada, Britain, and the United States planned in March 1949. Additionally, the transportation, logistic divisions, and the Army General Staff questioned the capability of the industry, logistics, and transportation resources to support the active service of a heavy tank.

The Tripartite Conference was meant for Canada, the USA, and the UK to establish certain requirements for tanks, like retaining the light, medium, and heavy tank classes. The conferences focus on simplicity, maintenance, economy, high production rate, low cost, reduced weight, and reliability. The idea for the medium and heavy tanks was that the UK and US developers designed separate guns, ammunition, and chassis and then conducted tests to determine the best. The results were to be combined into a single vehicle. This never really happened except for the specifications of the heavy tank.

Lieutenant Colonel Walter B. Richardson
Source: https://www.findagrave.com/memorial/7576413/walter-brown-richardson

Luckily for the T43, a previously mentioned advocate of the heavy tank, Lieutenant Colonel Arthur Stuart from the Marine Corps, was part of the Ordnance Technical Committee and thus in the ideal position to push for the introduction of the T43 heavy tank. Additionally, the Marine Corps advocate was supported by Lieutenant Colonel Walter B. Richardson from the Army, who was a veteran tank commander. Both services could count on support for the development of the T43 from both studies and policy boards.

On February 18th, 1949, an advisory board from Army Field Forces endorsed the heavy tank and also designated the heavy tank as the new main anti-tank weapon of the US Army, which meant the end of the tank destroyers in the US Army. The board then specified the required amount of heavy tanks. One battalion of each armored division (which consisted of 4 battalions in total) became a heavy tank battalion fielding 69 T43 tanks. The board determined the need for 12 divisions which were to be immediately mobilized in the case of war (1,476 heavy tanks), which would eventually grow to a full fighting force consisting of 64 armored divisions in the case of World War 3 (to put this into perspective, the US Army only fielded 20 armored divisions in WW2), resulting in a grand total of 11,529 T43 heavy tanks (in comparison, Germany only built a combined number of around 1,800 Tiger 1 and Tiger 2 tanks during World War 2). The chairman of the advisory board, Major General Ernest N. Harmon, also stated that:

‘’Unless our tank development situation is improved, we cannot expect to have enough tanks to support a major ground conflict for at least two and a half years after an emergency is declared to exist.’’

The Marine Corps formed their own Armor Policy Board on April 15th, 1949, to determine the requirements and usage of tanks in the cold-war era doctrine. Created through the efforts of Arthur J. Stuart, the board consisted of veteran battalion commanders of the war in the Pacific. The board determined that a heavy tank was desirable to provide support to the medium tanks during landing operations in the case of an armored counter-attack and to assist in the destruction of heavy fortifications. The board determined that three heavy tank battalions were needed in a wartime situation, but none during peacetime. To keep a trained manpower pool, a number of heavy tanks had to be acquired and combined with armored divisions in times of peace so that the crews were still able to train on the vehicle. Eventually, the Marine Corps put out a requirement for 504 heavy tanks, of which 55 were to be reserved for the three heavy tank battalions and 25 for training purposes, while the rest served as reserves.

After various reviews, the general staff approved the development and production of pilot vehicles on May 19th, 1949. Not long after the approval by the Army, the Marine Corps made their own order for additional pilot vehicles as well.

The T43 starts taking shape

Not long after the approval for pilot vehicles, the use of an elliptically shaped hull and turret, designed by Engineer Joseph Williams, was proposed. The elliptical shape improved the armor-to-weight ratio of the T43 by presenting highly angled armor with decreasing actual armor thickness the more angled the armor got and thus lessening the armor needed to provide 10 inches (254 mm) of effective armor. The appearance of the T43 changed and the new design was studied during conferences at Detroit Arsenal in October and December 1949. These conferences drastically altered the specifications of the T43.

Mock-up of an early version of the T43 without the remote-controlled machine gun blisters.
Source: Firepower, Hunnicutt

The turret ring was to be broadened from 80 inches to 85 inches in diameter (2,032 mm to 2,159 mm), the crew increased to 5 crew members by adding a loader because the planned automatic loading equipment was part of a different project, the elliptically shaped armor reduced the estimated weight to 55 US tons (49.9 tonnes) and a periscopic sight was added as a backup for the gunner’s rangefinder. The commander received gun controls to enable him to override the gunner and aim at a different target if necessary. Additionally, with the introduction of a second loader, an electric loader safety was added in order to move the second loader away from the recoiling breach when the gun was fired. A new concentric recoil cylinder was chosen to replace the previous three-cylinder recoil system. Other additions were the installation of an auxiliary engine-generator to enable the operation of the electrical systems without the main engine running, specifying quick-change barrels for the main gun, a cant-corrector for increased accuracy, and vane sight to help reorientation. The T140 gun mount was reduced in size and could accommodate a pair of .30 or .50 caliber machine guns. Various components were eliminated, including the .30 caliber remote-controlled blister machine guns, the gunner’s direct sight telescope, the panoramic telescope, and the lead computer. These changes were published on April 24th, 1950 and approved by the Army Staff on June 28th, 1950.

In addition, an OCM published on July 19th, 1950, mentions the development of multiple bulldozers for multiple tanks, including a bulldozer blade, designated T18, for the T43 Heavy Tank. Another OCM, published on August 17th, 1950, mentions the development of multiple flotation devices, including device T15, which was meant for the T43.

The US Army Tank Crisis

While the Americans were busy designing, developing, and adjusting their tank designs for a future war, the war came to them. Across the Pacific, after a period of border clashes and disputes, on June 25th, 1950 at 0400 hours, the North Korean Army invaded South Korea. The ROK army was taken completely by surprise and, 3 days later, on June 28th, Seoul fell to the North Koreans. The North Korean army pushed the ROK Army and its allies back to the Busan Line in August, which the United Nations managed to hold and eventually turn the tables after the Incheon Landing on September 15th, 1950.

Like the South Koreans, the Americans were also taken completely by surprise when the North Koreans invaded the South. Although reports had suggested a possible invasion, these were mostly ignored, as Korea was not seen as a likely theatre of war by the Western ministries compared to other possible theatres. The US and its allies feared that the Korean War would lead to the beginning of a new World War in which the West faced off against the East, a war which the US was ill-equipped to fight.

In June 1950, the Army’s Armored Panel reported that the Army and the Marine Corps had a combined number of 4,752 battle-worthy and in total 18,876 tanks. The Soviet Union had an estimated number of 40,650 tanks, of which an estimated 24,100 tanks were identified as reserves. Additionally, the Panel stated that the Soviet tanks were ‘’superior to any we now have.’’ Combine this with the previously mentioned statement of Major General Ernest N. Harmon in February 1949, which stated that the US could not expect to have enough tanks to support a major ground conflict for two and a half years after an emergency was declared, it can be concluded that the situation in which the US Army found itself in when the Korean War broke out was very dire.

Thus, the US Army had to go to war in Korea with outdated World War 2 equipment and, in addition, might have had to fight a new World War in which the outnumbered US tanks would have to face off against IS-3 heavy tank among other Soviet tanks. In response, the US Army Field Forces declared a Tank Crisis on July 12th, 1950. This Crisis was followed with a Crash Program to develop and produce the new generation T41, T42, and T43 tanks by any possible and plausible means, while, at the same time, refitting and refurbishing the US Army’s stock of World War 2 M4 Shermans and M26 Pershings. The US knew of the issues that a Crash Program could bring during the development, in the form of design problems and delayed fielding of the vehicles because of rapid design without proper testing, but the situation had such urgency that they accepted the risk. Between the declaration of the Tank Crisis and the armistice between North and South Korea on July 27th, 1953, the US funded 23,000 and produced 12,000 tanks.

Keeping the T43 project alive

When the Korean War broke out, the T43 existed only as a full-scale wooden mockup. Even worse for the T43, various parties within the Army were considering the cancellation of the T43. The Ordnance Department redefined military characteristics on April 24th, 1950, before the outbreak of the Korean War, which had made the T43 a less relevant project. In the spring of 1950, the Army Chief of Staff General, Joseph Lawton Collins, was making published statements on the supposed imminent obsolescence of the tank, with medium and heavy tanks in particular.

The earlier mentioned Ordnance Technical Committee member, US Army Lieutenant Colonel Walter B. Richardson, would also reveal a three-way struggle within the Army to his fellow committee member of the Marine Corps, Lieutenant Colonel Arthur J. Stuart. This struggle between the Infantry, Armor, and Ordnance branches was over the T42 medium tank project, with the Infantry desiring greater anti-tank performance from the 90 mm gun. The Logistics Division of the Army had presented a study to General Joseph Lawton Collins, with the recommendation of canceling the T43, as the national war economy would have severe difficulties in producing sufficient numbers of heavy tanks to equal Soviet stocks and production. Additionally, it was also expected that the experimental HEAT ammunition of the T42’s 90 mm gun could penetrate the armor of the Soviet heavy tanks.

In September 1950, the Detroit Arsenal conducted a study to arm the T43 with the T15 90 mm gun in a smaller turret. The new design reduced costs and weighed around 45 US tons instead of 55 US tons (40.8 tonnes instead of 49.9 tonnes). The T15 90 mm was an experimental upgrade mounted on the M26 Pershing around 1945 in the form of the T26E4. The T15 was a two piece ammunition gun which could penetrate 6.2 and 9.2 inches at 1,000 yards at 30 degrees (157.5 mm and 233.7 mm at 910 m), with a muzzle velocity of 3,200 and 3,750 fps (975 m/s and 1,143 m/s) for the AP and the HVAP rounds, respectively. The US Army discontinued developing a Pershing with the T15 90 mm gun because of practicality reasons which limited the performance of the vehicle. This study seems to have been initiated by advocates of the 90 mm gun with the Army Staff, but the exact reasons for this study remains vague except to reduce weight and costs of the T43.

A mockup of the early T43, according to Hunnicutt. According to Kenneth Estes, this was a mock-up of a T43 armed with a 90 mm gun.
Source: Firepower, Hunnicutt

Although the Army Chief of Staff and the Logistics Division were in favor of cancelling the T43, various forces within the Army would see to it that the T43 was ordered for production. The Army Field Forces were strongly opposed to the Army Chief of Staff for the following reasons. The 90 mm HEAT ammunition was unproven, the HEAT round could easily be defeated by spaced armor, which reports suggested that the Soviets were using, the round would be inaccurate after 1,000 yards (910 m) and even though a medium tank capable of defeating all enemy armor could be delivered, heavy frontal armor was still necessary to perform breakthrough or defensive operations.

Lieutenant Colonel Arthur J. Stuart also used these arguments when he wrote to his superiors of the Marine Corps to solidify their support. This resulted in a letter from the Marine Corps staff on April 20th 1950 to the Naval Planning Group, that the Marine Corps had no heavy tanks and that these were needed to provide defense against enemy armor.

Brigadier General Bruce C. Clarke
Source: US Army

When the Korean War began, the two Lieutenant Colonels also received support from the Armor Branch of the US Army. Brigadier General Bruce C. Clarke, the former assistant commandant of the Armor school and former member of the 1949 Army Field Forces Advisory Panel, which heavily endorsed the adoption of the T43. He had observed the Soviet build-up of forces in Europe while commanding a brigade in West Germany. He responded by calling for the ‘’immediate initiation of quantity heavy tank production.’’ With the support of the Army Field Forces, Brigadier General Bruce C. Clarke, and the endorsements of all the Army General Staff, the Army Chief of Staff had no other choice than to approve limited heavy tank production and the activation of a limited number of heavy tank battalions for evaluation in August 1950.

Lieutenant Colonel Walter B. Richardson learned that just 80 T43 tanks were approved for production and urged Lieutenant Colonel Stuart to make the Marine Corps support of the T43 project clear, so as to get more leverage for full heavy tank production. Three General Staff members of the US Army contacted Arthur J. Stuart, urging the Marine Corps to reveal their stance on the T43. As a result, the commandant of the Marine Corps wrote a letter to the Army Chief of Staff on September 15th 1950, to notify him of the Marine Corps requirement for a heavy tank and he requested whether production was planned for a heavy tank and what the estimated costs would be.

On November 7th 1950, a new designation system was implemented. Rather than classifying tanks by their weight in the light, medium and heavy categories, the tanks were now classified according to their main armament. In this case, the Heavy Tank T43 became the 120 mm Gun Tank T43.

The Army Staff confirmed their order in December 1950 for the production of 80 T43 tanks. In turn, the Marine Corps confirmed their order of 195 T43 tanks on December 20th 1950, which was later increased to a total of 220 heavy tanks costing $500,000 each (close to $5.4 million in 2019). An order of 300 T43 heavy tanks was placed with the Chrysler Corporation by the US Army and Marine Corps, in addition to six pilot vehicles which were already ordered on January 18th 1951.

The first T43 was completed and delivered to the Aberdeen Proving Ground in June 1951.

120mm Gun Tank T43

The 6 prototype versions differed from each other in multiple ways. The sources only mention specific details on the pilot vehicles #1, #3 and #6. These 6 pilot vehicles were also significantly different from the actual production vehicles. These differences in between the pilot vehicles included the main gun, sand shields, a pistol port, a ladder, muzzle brakes and driver periscopes, among others. The first two pilot vehicles were made according to the initial drawings and the other four according to early production drawings. The design of the final three pilot vehicles was carried out by Chrysler. The 6 pilot vehicles are essentially divided in two versions: the first 2 Pilot vehicles and the later 4 pre-production vehicles, of which the last 3, designed by Chrysler, were designated as 120mm Gun, Tank T43E1 on July 17th 1952. This was done because the differences between the initial T43 Pilot vehicles and the final three pre-production vehicles was large enough to obtain a new designation.

Some key features of the pilot vehicles which were removed on the production vehicles included a two armed gun travel lock, exhaust deflectors to prevent the suction of hot exhaust gasses in the engine cooler, exhaust pipes from the personal heaters through the hull and a track tensioning idler in front of the sprocket.

120mm Gun Tank T43, Pilot #1

Overview

T43 Pilot #1 weighed approximately 55 US tons unstowed and 60 US tons combat loaded (49.9 and 54.4 tonnes respectively). The vehicle was 22.94 feet (7 m) long without including the gun, 12.3 feet (3.75 m) wide and 10.56 feet (3.22 m) tall. The T43 was an impressive tank to see. The tank was operated by a five-man crew, consisting of the Commander (turret rear), Gunner (turret rear, in front of the Commander on the Commander’s right side), two Loaders (middle fighting compartment) and the Driver (front hull). The turret had two hatches, one for the commander and one for the loaders and the gunner.

T43 Pilot #1, note the pistol port on the side of the turret. Taken at Aberdeen Proving Ground July 7th 1951.
Source: Firepower, Hunnicutt

Hull

The hull was a mix of an elliptically shaped cast (mild steel, casted by General Steel Castings Corporation) and rolled steel which was assembled by welding. An elliptical shape is one of the most efficient ways to make a hull with maximum curvature across the front and sides, putting maximum actual armor where it is needed (the least angled parts of the armor). The armor is most vulnerable head on, but the more the projectile hits to the side of the armor, the more effective the armor gets because the angling gets steeper. The extreme angling of the elliptical shape also makes it more likely for a projectile to deflect if it does not hit the armor head on.

The front hull upper glacis presented 5.0 inches (127 mm) of armor at an angle up to 60 degrees vertically. This gave the T43’s upper glacis a minimal effective thickness 10 inches (254 mm) at every angle. The armor at the transition from the upper to the lower glacis was thicker than 5 inches (127 mm), the exact thickness is not specified by the sources. The advantage of an elliptical hull is that the armor is highly angled at every point and gets more effective the more away from the middle the shell hits the elliptical shape. The lower glacis was 4 inches thick, angled at 45 degrees from vertical. The minimal effective thickness of the lower glacis was around 7.1 inches (180.3 mm).

The front of the elliptically shaped hull of the T43, the first vehicle to implement this technique.
Source: Firepower, Hunnicutt

The sides of the T43 had an elliptical shape, like the front of the hull. Both the upper and lower glacis of the side armor presented armor equalling 3 inches (76.2 mm). The armor of the upper glacis was angled at 40 degrees from vertical, which meant it presented around 2.3 inches (58.4 mm) of actual armor. The side hull lower glacis was angled at 30 degrees from vertical, which meant it presented around 2.6 inches (66 mm) of actual armor. As with the frontal armor, the actual armor was thicker at the transition point from the upper to the lower glacis, but the exact thickness is not specified by sources.

The side of the elliptically shaped hull of the T43.
Source: Firepower, Hunnicutt

The rear of the hull was not elliptically shaped, like the front or the sides of the hull. The upper rear armor plate was 1.5 inches (38.1 mm) thick at 30 degrees vertical. This gave it an effective protection of around 1.73 inches (43.9 mm). The lower rear armor plate was 1 inch (25.4 mm) thick at an angle of 62 degrees vertical, which presented an effective armor of 2.13 inches (54.1 mm).

The floor of the T43 was, like the front and the sides, elliptically shaped. An advantage of an elliptically shaped floor is that it better deflects the blast of a mine because of its curved shape. The floor armor of the T43 lessened gradually from 1.5 inches (38.1 mm) at the front, to 1 inch (25.4 mm) in the center and 0.5 inch (12.7 mm) in the rear of the hull. The top of the hull was 1 inch (25.4 mm) thick.

The gun travel lock was located at the right of the rear hull plate. An interphone control box was located on the left side of the rear hull plate. Two storage boxes were located on both fenders, one large and one smaller. Two outlets were located at the upper right side of the hull (near the turret ring). These were outlets for the bilge pump and exhaust pipe for the personnel heater. The T43 had two pairs of lamps installed on the front of the hull. On the left side was a combination of a headlamp and horn and, on the right side, a blackout lamp (for convoy driving) and a headlamp. Additionally, a blackout marker was installed on both sides.

The headlight design of the first pilot vehicles on the top picture and the exhaust pipes of the personnel heater and bilge pump on the bottom picture.
Source: Firepower, Hunnicutt

The driver was located at the front of the hull, in the middle. The driver used a mechanical wobble stick to steer the vehicle, which was situated between the driver’s legs. At his feet were the brake (left) and accelerator (right) pedals. The horn button and primer pump were situated at his left and a handbrake lever on his right. In front of the driver were a performance indicator, an instrument panel, periscopes (T36 periscopes for the first 4 pilot vehicles), and a hand throttle lock. The seat could be tilted to the side and locked in place with the help of a lever and a clamp. Underneath the seat was an escape hatch for the driver, which was opened by pulling the hatch release lever, after which it would fall open. The driver’s hatch was a sliding hatch that would slide to the side when opened. Behind the driver were the fighting compartment, turret, and engine.

The driver’s compartment.
Source: Firepower, Hunnicutt

Mobility

The T43 was powered by the gasoline 12 cylinder AV-1790-5C engine. This air-cooled engine developed an 810 gross horsepower at 2,800 rpm and a net 650 hp at 2,400 rpm, which gave the vehicle a net horsepower to ton ratio of 10.8. The T43 used the General Motors CD-850-4 transmission, the same transmission that was used for the M46, M47 and M48 Patton tanks, which had 2 gears forward and 1 for reverse. Combined, this powerpack gave the T43 a top speed of 25 mph (40.2 km/h) on a level road. It had a fuel capacity of 280 gallons which gave it a range of approximately 80 miles (130 km) on roads.

The T43 used a torsion bars suspension with 7 road wheels and 6 return rollers per track. In addition, the T43 had a compensating idler at the front of the tracks and a track tensioning idler in front of each sprocket. It had 3 shock absorbers fitted on the first 3 road wheels and 2 on the last two road wheels. The T43 had 13 teeth and 28.802 inches (731.57 mm) diameter drive sprocket at the rear of the vehicle.

The lower hull of the T43, note the track tension idler before the sprocket, a feature only used in the pilot vehicles.
Source: Firepower, Hunnicutt

The T43 could use either the T96 or T97 tracks and had 82 track links per side. The tracks were covered by a small side skirt. The tracks had a width of 28 inches (711.2 mm) and a ground contact length of 173.4 inches (4.4 m). This gave the T43 a ground pressure of 12.4 psi (8,500 kPa). For comparison, a human foot has an average ground pressure of 10.15 psi (7,000 kPa). The tank had a ground clearance of 16.1 inches (409 mm) and the ability to climb a 27 inch (0.686 m) vertical wall. It could cross trenches of up to 7.5 feet (2.29 m) wide, could climb a 31-degree slope, and ford 48 inches (1.219 m) of water. The T43 was able to pivot steer as well.

Turret

The T43’s turret was a single steel casting. Like the hull, it was cast in an elliptical shape. The front of the turret was the most armored part and the thickness gradually decreased from the front to the rear of the turret. The gun mantlet had a thickness from 10.5 to 4 inches at a degree from 0 to 45 degrees vertical (266.7 mm to 101.6 mm). At its thinnest, this would give the T43’s gun mantlet a minimal effective armor of 5.66 inches (143.76 mm). The front of the turret had 5 inches (127 mm) of armor at 60 degrees vertical, which gave it an approximate effective armor of 10 inches (254 mm).

As previously stated, the side armor gradually lessened from the front to the rear of the turret. The side armor lessened from approximately 3.5 inches to 2.5 inches and was sloped at an average of 40 degrees vertical (88.9 mm to 65.5 mm). Pilot turret number 6 was tested by Aberdeen Proving Ground between September 8th and 17th 1952. This was done by firing 120 mm AP T116 ammunition (the ammunition the T43 would use) on the front (avg. 4.73 inches, 120.14 mm) and the frontal sides (avg 5.25 inches, 133.35 mm, 30 degrees longitude) of the turret, 90 mm AP T33 and 90 mm HVAP M304 ammunition at the frontal sides (avg. 3.63 and 3.46 inches respectively, 92.2 mm and 87.88 mm, 30 degrees longitude), 76 mm APC M62A1 and 57 mm AP M70 ammunition at the sides of the turret (avg. 3.28 to 3.10 inches, 83.31 to 78.74 mm, 90 degrees longitude).

Turret test of the T43 pilot turret.
Source: Aberdeen Proving Ground

The following observation was made: there were large differences in protection from a direct frontal attack as compared to a 30-degree flank and that this condition could be somewhat improved by a slight change in the turret wall thickness to increase its protection. The wall thickness decreased rapidly from the front to the sidewall areas and could be much improved by making this decrease more gradual.

A picture that represents the gradual lessening of armor from the front to the rear.
Source: Aberdeen Proving Ground and author

The rear of the turret had 2 inches (50.8 mm) of armor at 40 degrees vertical, which gave it an effective armor of approximately 2.61 inches (66.29 mm). The turret had 1.5 inches (38.1 mm) of armor at 85 to 90 degrees vertical. An armor plate was bolted on the turret at the gun’s position to facilitate the removal of the gun. Additionally, an armor plate was bolted on the top of the turret in front of the commander’s hatch and above the gunner. The back-up periscope of the gunner was installed on the top left of the armor plate. The loaders and the gunner had to share just one escape hatch, while the commander had his own. The safety of the loaders and the gunners when they needed to escape the vehicle seems questionable to say the least.

Top view of the T43 Pilot #1, note the loaders and gunner escape hatch in the middle right of the turret.
Source: Firepower, Hunnicutt

The commander was located in the rear of the turret, the gunner was located in front of the commander on the commander’s right side and the two loaders were located at the front of the turret at both the left and right side. To accommodate the gunner’s seat, a decrease was designed in the turret bustle which can be identified by a weird bulge at the bottom of the turret.

Commander’s seat of the T43.
Source: Firepower, Hunnicutt

External features of the T43 Pilot #1 turret included a pistol port on the left side wall, a ladder on the right side wall, a handrail on both sides, a handrail on the rear, a stowage rack on the rear, mounting for a jerry can on both sides at the rear of the turret, the protective blisters of the T42 rangefinder sticking out on both sides at the middle of the turret, a ventilator inlet on the left side of the commander’s cupola, two receptacles for radio antennas on both sides of the commander’s cupola and multiple lifting eyes on the front and the rear of the turret.

The commander’s cupola is an interesting development of the T43 heavy tank. The T43 pilot vehicles received the same commander cupola as the M47 Patton, but the production vehicles would receive the M48 Patton commander cupola which was designed by Chrysler, which was smaller than the early type commander’s cupola. It is unclear if the switch from the early type M47 Patton cupola to the M48 Patton cupola was carried out after the production of the 6 pilot vehicles or if this was done during the production of the pilot vehicles, as the last pilot vehicle, Pilot #6, seems to have the M48 Patton cupola. It might be that this switch was already carried out when Chrysler took over the design responsibility of the final three prototype vehicles, but sadly, no pictures of the Pilot #4 or #5 have been found to give support to this theory.

Early production commander’s cupola(top) and production commander’s cupola(bottom)
Sources: Firepower, Hunnicutt and http://afvdb.50megs.com/usa/pics/m103heavy.html

Armament

The T43 Pilot #1 was the only T43 pilot to be armed with the 120 mm T122 gun in the T140 combination gun mount. Every vehicle produced after Pilot #1 used the 120 mm T123 gun. The 120 mm T122 was a rifled gun barrel with a length from muzzle to breech block of 302.3 inches (7.68 m) and the barrel itself was 60 calibers or 282 inches long (7.16 m). The T122 could handle a 38.000 psi (262 mPa) pressure.

T43 Pilot design from the Fort Benning archives, provided by Sofilein.
Source: Fort Benning

Interestingly enough, it seems that Hunnicut has made an error in his sketch of the T43 Pilot #1 in his book: Firepower: A history of the American heavy tank. Hunnicut presents Pilot #1 with the muzzle brake of the 120 mm T53 gun, but without a bore evacuator. Since the later T34 Heavy Tanks were armed with 120 mm cannons with bore evacuators, it would be illogical for a gun of this size and with the technology available, to not have a bore evacuator. In addition, a picture from the Fort Benning archives shows a sketch of the T43 Pilot design with a bore evacuator.

Side drawing of the T43 Pilot #1, note the 120 mm T53 gun without a bore evacuator.
Source: Firepower, Hunnicutt

What is interesting about Pilot #1, is that it seems to never have had the actual T122 barrel as it was intended. Instead of a muzzle brake and bore evacuator, it seems to have a counterweight. A reason for not mounting a proper T122 gun might be because they never intended to test-fire the T43 Pilot #1, because the T43 would never use the T122 gun. Why the T123 gun was never mounted on Pilot #1 in the first place, is unknown. It is possible that the T122 gun was the only available gun at the time and a prototype was needed before a T123 gun could be supplied.

A picture of the T43 Pilot #1 without a tarp covering the Counterweight.
Source: https://mcvthf.org/Book/ANNEX%20G-4.html

The turret had an electric-hydraulic and manual 360-degree traverse. Additionally, it also used electric-hydraulic and manual elevation, with a range of -8 to +15 degrees. It took 20 seconds for the turret to fully traverse and the gun could elevate 4 degrees per second. The gunner aimed the main gun via the T42 range finder and had a T35 periscope as a backup. The Commander had a set of gun controls and was able to override the Gunner and fire if necessary. In short, the T43 had primitive Hunter-Killer capabilities.

Just two types of ammunition were developed for the T122 gun before its cancellation. These were an AP and an HVAP shot. Both shells were two-case ammunition. The right side loader would load the projectile and the left side loader would load the propellant and slide the ammunition into the gun breech. Before the gun could be fired, the left side loader had to step away from the gun and press the button of an electrical loading safety mechanism, so he would not get in the way of a recoiling 6,320 pound (2,870 kg) gun. The AP projectile and the propellant both weighed 50 pounds (22.67 kg), which meant that the left side loader had to slide a 100 pound (45.36 kg) round into the gun breach. The AP projectile of the T122 had a muzzle velocity of 3,100 fps (945 m/s), which could penetrate approximately 7.8 or 8.4 inches (198.1 mm or 213.4 mm) of armor at 30 degrees at 1,000 yards (910 m) depending on sources. The HVAP projectile could penetrate an estimated 14.5 or 15 inches (368.3 mm or 381 mm) of armor at 30 degrees at 1,000 yards (910 m), depending on sources. The maximum rate of fire was 5 rounds per minute and the T43 carried 34 rounds of 120 mm ammunition. Additionally, the T43 Pilot #1 could mount 2 coaxial .50 cal machine guns in the combination gun mount, one on each side of the main gun, and carried 4,000 rounds of .50 cal ammunition. One of the .50 cals could also be swapped with a .30 cal machine gun.

Other Systems

The electrics were powered by the main engine-driven main generator, which produced 24 volts and 200 amperes. An auxiliary generator was used when the main engine was not running. This auxiliary generator produced 28.5 volts and 300 amperes. In addition, a total of 4 12 volts batteries were available, divided in 2 sets of 2 batteries. These batteries were charged by either the main or auxiliary generator.

The T43 Pilot #1 used an AN/GRC-3, SCR 508 or SCR 528 radio, which was installed in the turret. It had 4 interphone stations plus an external extension kit.

The vehicle also had 2 personnel heaters on both sides of the front hull and 3 10-pound CO2 fixed fire extinguishers and 1 additional 5-pound portable CO2 fire extinguisher.

The 120mm Gun Tank T43, Pilot #1 still exists.

The T43 Pilot #1, restored and preserved at Fort Benning in 2020, picture taken by Sofilein.
Source: Sofilein

120mm Gun Tank T43, pre-production Pilot #3

The T43 Pilot #3 was a little different from T43 Pilot #1. The T43 Pilot #3 was, for example, armed with the T123 main gun in the T154 gun mount, which could handle a pressure of 48,000 psi instead of 38,000 psi of the T122 (3,310 Bar instead of 2,620 Bar), making it much more powerful. Its AP round could penetrate an estimated 9.2 inches (233.7 mm) of armor at 30 degrees at 1,000 yards (914.4 m) with a muzzle velocity of 3,300 fps (1,006 m/s). Its HEAT round could penetrate an initially estimated 13 inches (330.2 mm) of armor at all ranges at 30 degrees with a muzzle velocity of 3,750 fps (1,143 m/s) and, later, 15 inches (381 mm). The T123 gun has an effective range of 2,000 yards (1828,8 meters).

The pistol port and the side skirts were removed on Pilot #3.

The T43 Pilot #3 loaded on a train wagon.
Source: Firepower, Hunnicutt

120mm Gun Tank T43E1, pre-production Pilot #6

The 6th pilot vehicle was the Marine Corps pilot vehicle and was the last of the pilot vehicles. This pilot vehicle was, in contrast to the Pilot #1 and #3 vehicles, designed under the responsibility of Chrysler. Some notable differences from the previously mentioned pilot vehicles were the M48 style commander’s cupola instead of the early type M47 Patton one and the headlight guards. In the previous pilot vehicles, these were much more rectangular, but the headlight guard on the Pilot #6 was round. This shape would be used in all the production vehicles. Another distinct feature of Pilot #6 was the T-shaped muzzle break.

The T43 Pilot #6, note the headlight protectors and the T-shape muzzle brake.
Source: M103 Heavy Tank, Kenneth Estes

Pilot Vehicle Gallery

From top to bottom: T43 Pilot #1, T43 Pilot #3, and T43 Pilot #6. Note the differences like the pistol port and Commander’s cupola.

Meanwhile, in the Soviet Union

What the Western Allies did not know was that, after the initial reveal of the IS-3 during the 1945 Berlin Victory Parade, the IS-3 “super” tank had numerous mechanical issues. The design had been rushed into production, which resulted in welds cracking open on the thick frontal armor plates, the suspension had issues and also the engine mounts needed reinforcing. Large numbers of IS-3 heavy tanks were sidelined during an extensive upgrade program that lasted from 1948 to 1952. The IS-3 was produced until 1951, with a production number of around 1,800 tanks.

IS-3 tanks.
Source: T-10 Tankograd

In 1951, the British conducted a study of the effectiveness of the IS-3. In this study, they deemed that the IS-3 would have been more effective if it used either the German 88 mm KwK 43 of the Tiger II or the 85 mm D-5T gun. The 122 mm ammo was deemed too big and too unwieldy in the turret style of the IS-3. If one would compare the space of an IS-3 with that of a T43 Heavy tank, which achieved a maximum of 5 rounds per minute in a more spacious turret with two loaders, it can be concluded that the reload of the IS-3 and, thus, its effectiveness, would be less than its T43 counterpart.

While the Western Allies were still building their tanks to counter the IS-3, the Soviets were already designing its successor. In September 1949, the first prototype of the IS-5 or Object 730 was ready for trials. Although the eventual T-10 would differ slightly from the IS-5 because of various improvements that were made during production, the first vehicles of this new heavy tank were put into production on November 28th, 1953.

IS-5/Object 730 heavy tank.
Source: T-10 Tankograd

Conclusion

The T43 was the logical successor to American World War 2 heavy tank development. By building a lighter version of the T34 heavy tank and using the most advanced techniques at their disposal when it came to steel manufacturing, it was truly a worthy successor of the American heavy tanks. The elliptical hull shape gave the T43 better armor than the T34 while weighing 10 US tons less. Combined with a 48,000 psi gun, the T43 seemed to be the way to go to counter the Soviet IS-3 tank menace.

The problem is that the T43 always seemed to have been in a very tight spot and, even when the Korean War broke out, on the verge of cancellation. The first red flag would have been the ridiculous numbers that the Army suggested it needed, a massive 11,529 tanks for the US Army alone and an additional 504 tanks for the Marine Corps.

The second red flag was the division in the US Army on the T43, which will eventually cause the Army to drop out from bringing the T43E1 to the T43E2 standard and just go with the T43E1 instead. The Marine Corps was called in to bring the additional leverage needed for full-scale production of 300 vehicles, while the Marine Corps only requested about 4% of the total estimated number of about 12,000 tanks needed. With the Marine Corps ordering the most T43 tanks of the two branches, it can be suggested that the heavy tank developed by the Army and for the Army, was in actuality now a heavy tank for the Marine Corps instead. In short, the Army was already very divided on the T43 heavy tank, and thus the M103, before the first prototype was even built.

Luckily for the T43, enough leverage was given by the supporters within the Army and the Marine Corps to get the 6 T43 Pilot vehicles and the 300 production vehicles into production, 6 years after the IS-3 was revealed in Berlin and 1 year before the T-10, the successor of the IS-3, went into its first production run. But the future of the M103 Heavy Tank, albeit a troubled and extensive future, was secured by the supporters of the heavy tank in the Army and the Marine Corps.

Specifications (T43 Pilot vehicles)

Dimensions (L-W-H) 22.94 feet (without gun) x 12.3 feet x 10.56 feet (7 m x 3,75 m x 3,22 m)
Total weight, battle ready 60 US tons (54.4 tonnes)
Crew 5 (Driver, commander, gunner, two loaders)
Propulsion Continental 12 cylinder gasoline AV-1790-5C 650 hp net
Suspension Torsion bar
Speed (road) 25 mph (40 kph)
Armament 120 mm gun T122 (Pilot #1)
120 mm gun T123 (Pilot #2 to #6)
Sec. 3 .50 caliber MG HB M2 (two coaxial, one on turret top) or .30 caliber M1919A4E1 for one of the coaxial machine guns
Armor

Hull

Front (Upper Glacis) 5 in at 60 degrees (127 mm)
Front (Lower Glacis) 4 in at 45 degrees (101.6 mm)
Sides (Upper and Lower) 3 in at 0 degrees (76.2 mm)
Rear (Upper Glacis) 1.5 in at 30 degrees (38.1 mm)
Rear (Lower Glacis) 1 in at 62 degrees (25,4 mm)
Top 1 in at 90 degrees
(25.4 mm)
Floor 1.5 to 0.5 in at 90 degrees (38.1 mm to 12.7 mm)

Turret

Front 5 in at 60 degrees (127 mm)
Gun mantlet 10.5-4 in from 0 to 45 degrees (266.7 mm to 101.6 mm)
Sides 3.25-2.75 at 40 degrees (82.55 mm to 69.85 mm)
Rear 2 in at 40 degrees (50.8 mm)
Top 1.5 in from 85 to 90 degrees (38.1 mm)

Production 6 pilot vehicles

Special thanks to Lieutenant Colonel Lee F. Kichen, USA-Retired

Illustrations

The early design concept of the T43 Heavy Tank with remote control blister machine guns.
T43 Pilot #1
T43 pre-production Pilot #3
T43E1, pre-production Pilot #6

Thanks to Wisuru for supporting Tank Encyclopedia! If you’re interested in interesting biography podcasts, quizzes and other science and history articles, check out their website.

Sources

Archive Sources

Elements of Armament Engineering: Ballistics, Part 2
Standard Military Vehicle Characteristic Data Sheets
Aberdeen Proving Ground Firing Record APG File: 451.6/2, DA File: 470.4/APG
Guns for Heavy Tanks
Advisory Panel on Armor 334/44 August 19 1954
Army Operational Research Group Report 11/51 Performance of British and Russian Tanks
Fort Benning: R.P. Hunnicutt Collection with courtesy of Sofilein

Literature

R.P. Hunnicutt:
Firepower: A history of the American Heavy Tank
Patton: A History of the American Main Battle Tank

Kenneth W. Estes:
M103 Heavy Tank 1950-74
Marines under armor: The Marine Corps and the Armored Fighting Vehicle, 1916-2000

Lieutenant Colonel Lee F. Kichen, USA-Retired:
Private Correspondence
On Point, The journal of Army History, Volume 24, no. 4, Spring 2018

Max Hastings:
The Korean war

Technical Manuals:
TM 9-2350-206-12

Additional Sources

Camp Colt to Desert Storm
AFV Weapons 41: M103 Heavy Tank + M41 Light Tank(Walker Bulldog)
History of Acquisition in the Department of Defense, Volume 1
Intimidating the World: The United States Atomic Army, 1956-1960
Tankograd T-10
Tank-net.com
https://mcvthf.org/Book/ANNEX%20G-4.html
USMC History Division
The Chieftain’s Hatch: Improving Super Pershing

Categories
Cold War US Heavy Prototypes

120mm Gun Tank T57

U.S.A. (1951)
Heavy Tank Prototype – 2 Turrets Built

The T57 started life in the early 1950s. At this time, the 120mm Gun Tank T43 (which would become the M103) was well on its way to becoming America’s next heavy tank, but even before it had entered serialization, ideas began to circulate about future upgrades.
One such idea was the possibility of mounting an auto-loading device in the tank’s turret, and further study into this idea proved that such a device would be ill-suited to the T43’s turret. As such, concentration turned to a new turret design, which would be mounted on pivoting trunnions. In other words, designers began to consider the addition of a new technology at the time, an Oscillating Turret. Testing at the Aberdeen Proving Grounds (APG) had already proved that smaller caliber guns worked in such turrets. There was no reason that a larger caliber gun, such as the powerful 120mm, wouldn’t work in such a turret. A development program was initiated on October 12th, 1951, with the project receiving the designation of 120mm Gun Tank T57.

One of the earliest concepts of the T57. Photo: Presidio Press

Development

On 12th October 1951, a development program began to design a 120mm armed heavy tank with an Oscillating turret and automatic loader. Two pilot models were authorized, and the tank was designated as the 120mm Gun Tank T57. The turrets, each with 2.1 meter (85 inch) rings, were to be tested on the hull of the T43. Two hulls of which were earmarked for this purpose.
The initial design for the autoloader was for a cylindrical type mounted directly behind the breach of the gun in the turret bustle. However, it was predicted that the measurements of such a device would take up a space of 76 cm – 1 meter (30 – 42 inches) but this depended on whether the cylinder would hold 11, 9 or 6 rounds. Army Field Forces (AFF) rejected this design, stating that such equipment would end up with the turret bustle being overly large in overall dimensions, as well as in the overhang of the bustle.
To overcome this possible design flaw, a contract was drawn up with the Rheem Manufacturing Company to design and construct the two authorized pilot vehicles.

Another early concept of the T57

Turret

The Oscillating type of turret consists of two actuating parts, these were a collar that is attached to the turret ring, allowing horizontal traverse, and a pivoting upper part that holds the gun, loading mechanism, and crew. Both halves of the T57’s turret were cast in construction, utilizing cast homogeneous armor. Armor around the face was 127mm (5-inches) thick, angled at 60 degrees. The armor on the sides of the turret was slightly thicker at 137mm (5.3 inches) but was only 51 mm (2 inches) on the bustle.
The sides of the collar were bulbous to protect the trunnions that the upper half pivoted on, with the other half consisted of a long cylindrical ‘nose’ and a low profile flat bustle. The turret was mounted on the unmodified 2.1 meter (85 inch) turret ring of the T43 hull.

Cutaway views of the enternal systems and layout of the turret. Photo: Presidio Press
Though it looks as though there were two, there were actually three hatches in the roof of the T57. There was a small hatch on the left for the loader, and atop the commander’s cupola which featured five periscopes and a mount for a .50 Caliber (12.7mm) machine gun. These hatches were placed on top of the third hatch, which was a large square that took up most of the middle of the roof. This large hatch was powered and granted a larger escape route for the crew but also allowed internal turret equipment to be removed easily. In front of the loader’s hatch was a periscope, and there was another above the gunner’s position.
Behind the large hatch was the ejection port for spent cartridges. To the right of this was the armored housing for the ventilator housing. On each side of the turret were ‘frogs eyes’, the armored covers for the stereoscopic rangefinder used to aim the main gun.

Gun

The initial Rheem concept had the gun rigidly mounted without a recoil system in a cast, low silhouette Oscillating turret, with the gun protruding from a long, narrow nose. The gun featured a quick change barrel, which was which was similar to the 120mm Gun T123E1, the gun being trialed on the T43. However, for the T57, it was modified to accept single piece ammunition, unlike the T43 which used separately loading ammo. This new gun was attached to the turret via a conical and tubular adapter that surrounded the breech end of the gun. One end screwed directly into the breach, while the front half extended through the ‘nose’ and was secured in place by a large nut. The force created by the firing of the gun and the projectile traveling down the rifled barrel was resisted by rooting the adapter both the breech block and turret ring. As there was no inertia from recoil to automatically open the horizontally sliding breech block, a hydraulic cylinder triggered by an electric switch was introduced which would be engaged upon the firing of the gun.
This new variant of the T123 was designated the 120mm Gun T179. It was fitted with the same bore evacuator (also known as a fume extractor) and muzzle break as the ‘T123’. The gun’s rigid mount was designated the ‘T169’, making the official nomenclature ‘120mm Gun T179 in Mount T169’
In the oscillating turret, the gun could elevate to a maximum of 15 degrees, and depress 8 degrees. Projected rate of fire was 30 rounds per minute. The main gun had a limited ammunition supply due to the large size of the 1-piece rounds. The T43 hull had to be modified to allow storage, but even then, only 18 rounds could be carried.
It was proposed that two .30 Caliber (7.62mm) machine guns would be mounted coaxially. This was later reduced to a single machine gun placed on the right side of the gun.

Automatic Loader

The automatic loader used on the T57 consisted of a large 8-round cylinder located below the gun, and a ramming arm that actuated between positions relative to the breech and magazine. The loader was designed for 1-piece ammunition but an alternate design was prepared for use with 2-piece ammunition.
Operation: 1) The hydraulically operated ramming arm withdrew a round and aligned it with the breach. 2) The rammer then pushed the round into the breach, triggering it to close. 3) Gun is fired. 4) Effect of gun firing trips the electric switch that opens the breech. 5) Rammer picks up a fresh round, at the same time ejecting the spent cartridge through a trap door in the roof of the turret bustle.

A diagram of the loading process. Photo: Presidio Press
Ammunition types such as High-Explosive (HE), High-Explosive Anti-Tank (HEAT), Armor Piercing (AP), or Armor-Piercing Ballistic-Capped (APBC) could be selected via a control panel by either the Gunner or the Tank Commander (TC). The HEAT round could punch through a maximum of 330mm (13 inches) of Homogeneous Steel Armor.

Hull

The hull that was used for the project was the same as the 120mm Gun Tank T43, which would later be serialized as the M103, the US’ last heavy tank. Armor on the hull was unchanged. The cast “beak” was 100 to 130 mm (3.9-5.1 in) at the thickest.
An 810hp Continental AV1790 12-cylinder air-cooled gasoline engine propelled this chassis to a speed of around 21 mph (34 km/h). The tank’s weight was supported on seven road wheels attached to the torsion bar suspension. The drive sprocket was at the rear while the idler wheel was at the front. The idler wheel was of the compensating type, meaning it was attached to the closest roadwheel by an actuating arm. When the roadwheel reacts to terrain the idler is pushed out or pulled in, keeping constant track tension. The return of the track was supported by six rollers.

Line drawing of the complete T57, with OScilliating turret mounted on the T43/M103 hull. Photo: Presidio Press

Crew

The T57 had a crew of four men. The Driver’s position was standard for T43/M103 hulls. He was located centrally in the bow at the front of the hull. Arrangements inside the turret were standard for American tanks. The Loader was positioned at the left of the gun. The Gunner was on the right with the Commander behind him.

Fate

The T57 project eventually ground to a halt. Progress became slow due to delays in procuring some equipment from the US Government. This problem was due, in no small part, to changing opinions in tank design. Designers were moving towards lighter vehicles that retained powerful guns, instead of heavy (as in weight and class) tanks.
One of the two pilot turrets constructed by Rheem was trial fitted to a T43 hull. Work on the project, however, stopped before tests of the systems could take place. The United States Ordinance Committee officially canceled the project on January 17th, 1957. Both turrets were subsequently scrapped, and the T43 hulls were returned to a supply depot for future use.
The T57 did, however, live on in another tank project, but this time in the shape of a medium tank. This project was designated the 120mm Gun Tank T77. It was a project to mount the T57’s turret on the hull of the 90mm Gun Tank T48, the prototype of the M48 Patton III. Just one photo, a model, and blueprints exist.
The Rheem Company would also continue to design tank components for the United States Military. Other projects they worked on included the 90mm Gun Tank T69, and 105mm Gun Tank T54E1 projects. Both of which featured similar turrets and loading systems.

A small scale mock-up of the T57. Photo: Presidio Press

TE to the Rescue

In late-2017, a scale model of the T57 produced by Rheem appeared on the internet auction sight, eBay. This model had appeared a number of times on the website without being purchased. The model was made for Fort Benning Armored Force Command. It is made from solid aluminum and weighs nearly 22 pounds (10 kg), it is also 2 feet (70 cm) long.

The scale model of the T57 from when the item was put up for auction on eBay.
Rather than let the model fall into the hands of a private collector, and be hidden from view, the Tank Encyclopedia team decided to step in a secure its fate in partnership with the U.S. Army Armor & Cavalry Collection, Georgia, USA. A fundraiser was organized and launched by Andrew Hills of FWD Publishing – and one of our writers – on the website ‘GoFundMe’ in November 2018. The thinking behind this was that he (all of us) wanted to see the model get to its rightful home – a national collection where it could be enjoyed by future generations and help foster a greater understanding of the evolution of American armour.
By the end of 2018, we had raised the necessary $700 to purchase the model. Just as planned, it was sent to the Museum. It is now safe and sound, reserved for future generations to see.

The T57 model at the U.S. Army Armor & Cavalry Collection. Photo: AACC

Rendition of the T57 heavy tank in a fictional livery based on common styles from the era. Illustration by Alexe Pavel, based on an illustration by David Bocquelet.

An article by Mark Nash

Specifications

Dimensions (L-w-H) 37.4 (including gun) x 8.7 x 9.45 ft (11.32 x 2.6 x 2.88 m)
Total weight, battle ready 48.5 tons (96 000 lbs)
Crew 4 (Commander, Driver, Loader, Gunner)
Propulsion Continental AVDS-1790-5A V12, AC Twin-turbo gas. 810 hp.
Transmission General Motors CD-850-3, 2-Fw/1-Rv speed GB
Maximum speed 30 mph (48 km/h) on road
Suspensions Torsion bars
Armament Main: 120 Gun T179 Sec: 1 Browning M2HB 50. cal (12.7mm), 1 cal.30 (7.62 mm) Browning M1919A4
Production 2

Links & Resources

OCM (Ordnance Comittee Minutes) 34048
April 1954 Report from the Office of the Chief of Ordnance (PDF)
Presidio Press, Firepower: A History of the American Heavy Tank, R. P. Hunicutt

Categories
Cold War US Heavy Prototypes

120mm Gun Tank T77

U.S.A. (1951)
Heavy Tank Prototype – 2 Turrets Built

In October 1951, a heavy tank project was underway to mount an oscillating turret with an automatically loading 120mm Gun on the hull of the 120mm Gun Tank T43. (The T43 would later be serialized as the 120mm Gun Tank M103, America’s last heavy tank.). This was the T57, and the Rheem Manufacturing Company were granted a contract to design and build two pilot turrets and autoloading systems.
During the T57’s development, it became clear that it was feasible to mount a lighter armored version of the T57 turret on the hull of the 90mm Gun Tank T48 (The T48 later became the 90mm Gun Tank M48 Patton III). This combination granted the possibility of creating a ‘heavy gun tank’ that was lighter than any previously designed.
In May 1953, a development project was started to create such a tank. It would be designated the 120mm Gun Tank T77, and another contract was signed with Rheem to create two pilot tanks.

Hull

The hull chosen for the project was that of the 90mm Gun Tank T48. The tank weighed about 50 tons, with armor of up to 110mm thick.
The tank was powered by a 650 hp Continental AVSI-1790-6 V12, air-cooled twin-turbo gasoline engine. This would propel the tank to a speed of 30 mph (48 km/h). The tank was supported on a torsion bar suspension, attached to six road wheels. The drive sprocket was at the rear, while the idler was at the front. The idler wheel was of the compensating type, meaning it was attached to the closest roadwheel by an actuating arm. When the roadwheel reacts to terrain the idler is pushed out or pulled in, keeping constant track tension. The return of the track was supported by six rollers.

A small scale mockup of the T77. Photo: Presidio Press

Turret

The Oscillating type of turret consists of two actuating parts, consisting of a collar that is attached to the turret ring, allowing horizontal traverse, and a pivoting upper part that holds the gun, loading mechanism and crew. Both halves of the T57’s turret were cast in construction, utilizing cast homogeneous steel armor. Armor around the face was 127mm (5 inches) thick, angled at 60 degrees. This increased to 137mm (5.3 inches) of the sides of the turret and dropped to 51 mm (2 inches) on the bustle.*
*The T77’s turret was supposedly designed to be lighter by having thinner armor, however, Hunnicutt’s data shows it to be the same as the T57’s turret. Whether this is erroneous or not is unknown.
The sides of the collar were made to be round and bulbous in shape to protect the trunnions that the upper half pivoted on. The other half consisted of a long cylindrical ‘nose’ and a low profile flat bustle.

Cutaway views of the internal systems and layout of the turret. Photo: Presidio Press
Though it looks like two, there were actually three hatches in the roof of the turret. There was a small hatch on the left for the loader, and atop the turret, a commander’s cupola which featured five periscopes and a mount for a .50 caliber (12.7mm) machine gun. These hatches were placed on top of the third hatch, which was a large square which took up most of the middle of the roof. This large hatch was powered and allowed a larger escape route for the crew, but also allowed internal turret equipment to be removed easily. In front of the loaders, hatch was a periscope, there was another above the gunner’s position.
Behind the large hatch was the ejection port for spent cartridges. To the right of this was the armored housing for the ventilator. On each side of the turret were ‘frogs eyes’, the armoured covers for the stereoscopic rangefinder used to aim the main gun.

Gun

The initial Rheem concept had the gun rigidly mounted without a recoil system in a cast, low silhouette oscillating turret. The gun protruded from a long, narrow nose. The gun featured a quick change barrel, was basically identical to the 120mm Gun T123E1, the gun being trialed on the T43. However, for this turret, it was modified to accept single piece ammunition, unlike the T43 which used separately loading ammo. This new gun was attached to the turret via a conical adapter that surrounded the breech end of the gun. One end screwed directly into the breech, while the front half extended through the ‘nose’ and was secured in place by a large nut. The force created by the firing of the gun and the projectile traveling down the rifled barrel was resisted by rooting the adapter both the breech block and turret ring. As there was no inertia from recoil to automatically open the horizontally sliding breech block, a hydraulic cylinder was introduced. Upon firing the main gun this hydraulic cylinder was triggered via an electric switch.
This new variant of the T123 was designated the 120mm Gun T179. It was fitted with the same bore evacuator (fume extractor) and muzzle brake as the T123. The gun’s rigid mount was designated the T169, making the official nomenclature ‘120mm Gun T179 in Mount T169’
It was proposed that two .30 caliber (7.62mm) machine guns would be mounted coaxially. This was later reduced to a single machine gun placed on the right side of the gun.
In the oscillating turret, the gun could elevate to a maximum of 15 degrees, and depress 8 degrees. Projected rate of fire was 30 rounds per minute. The main gun had a limited ammunition supply due to the size of the 1-piece rounds. The T48 hull had to be modified to allow storage, but even then, only 18 rounds could be carried.

Automatic Loader

The automatic loader shared by the T77 and T57 consisted of a large 8-round cylinder located below the gun, and a ramming arm that actuated between positions relative to the breech and magazine. The loader was designed for one-piece ammunition but an alternate design was prepared for use with two-piece ammunition.
Operation: 1) The hydraulically operated ramming arm withdrew a round and aligned it with the breech. 2) The rammer then pushed the round into the breech, triggering it to close. 3) Gun fires. 4) Effect of gun firing trips the electric switch that opens the breech. 5) Rammer picks up a fresh round, at the same time ejecting the spent cartridge through a trap door in the roof of the turret bustle.

A diagram of the loading process. Photo: Presidio Press
Ammunition types such as High-Explosive (HE), High-Explosive Anti-Tank (HEAT), Armor Piercing (AP), or Armor-Piercing Ballistic-Capped (APBC) could be selected via a control panel by either the gunner or the tank commander (TC). The round could punch through a maximum of 330mm (13 inches) of Rolled Homogeneous Steel Armor.

Crew

The T77 had a crew of four men. The driver’s position was standard for T48/M48 hulls. He was located centrally in the bow at the front of the hull. Arrangements inside the turret were standard for American tanks. The loader was positioned at the left of the gun. The gunner was on the right with the commander behind him.

Fate

The T77 would share the same fate as other Rheem designed tanks such as the T69, T57 and T54. Like the T57, the T77’s development was arduously slow, and in 1957, the project was finally canceled by the US Ordnance Department. Both turrets were scrapped in February 1958.

An article by Mark Nash

Specifications

Dimensions (L-w-H) 20’10” (without gun) x 11’9″ x 10’10” ft.in
(9.3m x 3.63m x 3.08m)
Total weight, battle ready Around 48.5 tons (96 000 lbs)
Crew 4 (Commander, Driver, Loader, Gunner)
Propulsion Continental AVDS-1790-5A V12, AC Twin-turbo gas. 810 hp.
Transmission General Motors CD-850-3, 2-Fw/1-Rv speed GB
Maximum speed 30 mph (48 km/h) on road
Suspensions Torsion bars
Armament Main: 120 Gun T179 Sec: 1 Browning M2HB 50. cal (12.7mm), 1 cal.30 (7.62 mm) Browning M1919A4
Production 2

Links & Resources

OCM (Ordnance Comittee Minutes) 36741
Presidio Press, Firepower: A History of the American Heavy Tank, R. P. Hunicutt


Illustration of the 120mm Gun Tank T77 by Tank Encyclopedia’s own David Bocquelet.

Categories
Cold War US Heavy Prototypes

Chrysler K (1946)

U.S.A. (1946)
Heavy Tank Concept – None Built

The Chrysler K was an American heavy tank prototype designed in response to the increasing interest in heavy tanks at the end of the Second World War. The growth in interest was thanks, in no small part, to the discovery of German plans for super heavy tanks such as the Maus and E100. Most importantly, however, it was the appearance of the Soviet IS-3 at the Berlin victory parade in 1945 that really jump-started the process.

The appearance of the IS-3 sent a chill down the spine of all major allied powers. Each nation invested large amounts of time, energy, and resources in heavily armored tanks with powerful main armaments, not least the USA, whose only heavy tank was the M26 Pershing. This vehicle was considered to lack the required firepower and protection to face tanks such as the new IS-3.

One of these early designs was a submission from the Chrysler Motor Corporation. Called the ‘Chrysler K’, it would be armed with a 105 mm main gun, and armor up to 18 cm (7 inches) thick.

Soviet IS-3 Heavy Tanks at the Berlin Victory parade in 1945. This pike-nosed heavy tank was the catalyst for many western heavy tank designs. Photo: Wikimedia Commons

Background, the Stilwell Board

On 1st November 1945, the ‘Stilwell’ Board was convened, named after the man heading the meeting, General Joseph W. Stilwell. The official designation, however, was ‘War Department Equipment Review Board’. The findings of this board, submitted in a report on 19th January 1946, agreed, for the most part, with earlier recommendations that Light, Medium, and Heavy tanks should all be developed. However, experiments with Super Heavy tanks, such as the T28/T95, would be abandoned. Another omission from the report was the development of dedicated tank destroyers, following the Armored School’s (based at Fort Benning, Georgia) opinion that the best anti-tank weapon would be another tank. As such, a Heavy tank was favored in tank versus tank combat due to powerful guns and thick armor.

Chrysler’s Submission

The famous motor car company, Chrysler, based in Michigan, submitted their design for an unconventional Heavy tank to the Armored School in a presentation by a Mr. F. W. Slack at Fort Knox on 14th May 1946. It would be known as the ‘Chrysler K’. The origin of the ‘K’ may lie with Kaufman Thuma Keller, the president of the Chrysler Corporation from 1935 to 1950, and advocate of the creation of Detroit Arsenal (DA). It is quite possible that the tank was named after him, given his position at Chrysler, and his relationship with the military thanks to DA.

Kaufman Thuma Keller, President of the Chrysler Corporation 1935-1950. Quite possibly the man behind the ‘K’. Photo: mountjoyhistory.com

Design

Chrysler’s design would incorporate a number of features that were sophisticated for the period they were designed in. These included an electric motor, remote controlled secondary armaments, and a ‘Driver in Turret’ arrangement.

Armament

The 105 mm Tank Gun T5E1 was chosen as the main armament for Chrysler’s heavy tank. Designed in 1945, it was the popular choice for American Heavy tanks at the time and was also mounted on vehicles such as the Heavy Tank T29, and the Super Heavy Tank T28. The T5E1 had a medium velocity of 945 m/s (3,100 ft/s). A variety of ammunition (which was two-part, separately loading. eg, projectile loaded then charge) allowed it to be as good a bunker buster as a tank killer, with the gun proving capable of penetrating concrete as well as metal. Ammunition types included APBC-T (Armor-Piercing Ballistic-Capped – Tracer), HVAP-T (High-Velocity Armor-Piercing – Tracer), (Armor-Piercing Composite Rigid – Tracer) APCR-T and HE (High Explosive). The APBC-T shell could penetrate 135 mm (5.3 in) of armor at a 30-degree slope or 84 mm (3.3 in) of armor at a 60-degree slope, 914m (1,000yd).

At 7.53 m (24 ft 8 in), the barrel of the weapon was rather long. It was concluded that if the turret was mounted in the usual place, ie, centrally, the gun would become hazardous in convoy travel or whilst maneuvering. As such, the decision was made to place the turret at the back of the tank, off-setting the length of the gun. This design choice resulted in the vehicle having an overall length of 8.72 m (28 ft 7.5 in). This is just 7.62 cm (3 in) longer than the M26, despite the 105 mm gun being 16.5cm (6½ inches) longer than the 90 mm gun of the M26. The gun could elevate up to 25 degrees, and depress to 4-degrees.

Secondary armament was machine gun heavy, with three .50 Caliber (12.7mm) heavy machine guns and two .30 Caliber (7.62 mm) machine guns. One of the .50 Cal. machine guns was mounted coaxially with the main gun, the other two were placed in secondary turrets on the left and right rear corners of the hull. They had a limited horizontal traverse, but could be elevated upwards to defend against air attack (quite how practical this was is debatable). The two .30 Cal. machine guns were placed in blisters at the left and right top corners of the upper glacis. It is unknown whether they were ball mounted and had a degree of traverse, or whether they were completely fixed. All of these weapons were controlled and fired via a remote control system that was an improved and simplified version of the turret control system on the B-29 Superfortress bomber. If they were fixed, it is debatable as to whether these weapons would’ve been any use at all. Fixed, forward mounted machine guns like these were abandoned from designs long before the ‘K’. As an example, the original versions of the Medium Tank M3 and M4 Sherman had fixed forward facing MGs, but not the later ones. The layout of Machine guns on the hull is similar to an Army Ground Forces (AGF) design for a medium tank.

Turret

One problem with the T5E1 gun was that it had a long breech. Still, the turret had to accommodate this, 100 rounds of 105 mm ammunition, and the crew which consisted of a commander, gunner, loader, and the driver. As a result of this, the turret diameter had to be wider than anything previously designed for an American tank. The internal diameter was 2.9 meters (9 foot 10 inches), while the turret ring was 2.1 meters (86 inches), as opposed to 1.75 meters (69 inches), the largest of previous designs. It stated that 100 rounds of the separately loading 105mm ammunition were carried by the tank and that they were stored circumferentially around the turret. However, an investigation into this reveals that there simply isn’t enough room for all 100 rounds inside. Though it isn’t stated in any source material, it is reasonable to suggest that ammunition was stored under the turret, as there is enough unaccounted for space from the bottom of the hull to the floor of the turret. As stated this is speculation but it is not unreasonable as it was a very common practice.

The turret was hemispherical in shape, and cast in construction – this shape offered excellent ballistic protection. The turret face was 18 cm (7 inches) thick, while the rest of the casting was 7.62 cm (3 inches) thick. Ammunition was stored circumferentially at the rear of the turret. The face of the turret was reinforced with a mantlet consisting of a large, thick disc. The exact diameter and thickness of this mantlet plate are unknown.

An unusual feature of the Chrysler, for the time, was the fact that the driver was located in the turret with the rest of the crew. It wasn’t the first time that a tank could be driven from the turret, however, as a remote control box in the turret of the T23 allowed control from within should the driver be knocked out. It was believed that having all the crew in the turret provided better communication and cooperation. The turret still had the ability to rotate 360-degrees. The driver’s seat (and presumably controls) were geared so that they were always linear (always facing forward in relation to the hull) to the tanks hull, no matter where the turret was pointing. His position was surrounded by pericopes so no matter where he was in relation to the turret, he would always be able to see where he was going.

The exact crew positions in the turret are unknown, but looking at the position of hatches and pericopes we can make an educated assumption. It would appear the Driver sat at the front left of the turret with the Loader behind him. The gunner sat at the front right, with the Commander at his rear.

A small-scale mock-up of the ‘K’ tank. This is as far as the project got. Note that the rear machine gun turret is traversed out slightly. Photo: Presidio Press.

Propulsion

With the turret moved to the rear of the tank, the engine would now take up the space left at the front end. The power requirements for the vehicle were based on a US Ordnance Department idea calling for 20 hp per-ton for this projected 60-ton tank. The gasoline-fueled engine was an unspecified design by Chrysler and was powerful with a projected output of 1,200 hp.

The engine was placed in the front end of the hull was to was to be connected to two electric motors that formed the tank’s final drives at the front of the vehicle. This system is similar to that used on the Medium Tank T23 prototype. The electric drive system on the ‘K’ tank was designed by a Mr. Rodger.

The engine system was fed by 600-US gallon (2727 liter) fuel tanks. The exact number of tanks is unknown, but it is likely to be at least two, judging by other American heavy tanks of the time.

Suspension

The suspension was the usual torsion bar type. There were eight twin road-wheels per side, with the idler at the back and the drive sprocket at the front. The idler was the same type of wheel used for the road wheels. The return of the track was not supported by rollers. This is known as a flat track suspension and is common on Soviet tanks such as the T-54 and so on. The track was 76.2 cm (30 inches) wide.

Hull

The hull was rather square in its overall shape, with the frontal plate 18 cm (7 inches) thick and angled at 30-degrees. Such angling brought the effective thickness up to roughly 36 cm (14 inches). Armor on the tank’s sponsons was less impressive being just 7.62 cm (3 inches) thick. They were sloped inwards slightly at around 20-degrees, this would’ve made the effective thickness 8.1 cm (3.1 inches). A 25 mm (1 inch) thick armored floor protected the underside of the vehicle. The tank was 3.9 meters (12 foot 8 inches) wide. For rail travel, the sponsons and outer halves of the road-wheels could be removed.

The overall height of the ‘K’ tank, turret included, was 2.6 meters (8 foot 8 inches) tall. This was 7.62 cm (3 inches) shorter than the M26. Altogether, the tank was projected to weigh 60 tons.

A modern side-on schematic of the Chrysler ‘K’ heavy tank concept. Photo: Tank Archives Blogspot

Fate

Funds for tank design gradually dwindled after the Second World War. As such, the Chrysler K tank never left the development stage, with only line drawings and a scale model produced. Unfortunately, the drawings and scale model are not thought to survive, and only a photo of the model remains. The project was abandoned, with attention turning to more conventional tank designs such as the Heavy Tank T43, which would eventually become America’s last heavy tank, the 120 mm Gun Tank M103.

Some of the design features of the ‘K’ tank were carried over into future tank projects. The ‘Driver in Turret’ concept was utilized on the M48 Patton based M50/53 self-propelled gun, and also the MBT-70 and subsequent prototypes. To the east, the Soviets also used this concept in their prototype medium tank, the Object 416.

The Other ‘K’

This heavy tank was not the only tank designed by Chrysler to bare the ‘K’ designation. Twenty-two years later, in 1968, Chrysler would put forward another design intended to be a possible upgrade of the 105mm Gun Tank M60. The design featured a brand new, comparatively smaller turret and a new main gun.

Two guns were tested on the tank. One of these was the 152 mm Gun Launcher XM150, a modified version of the gun used in the MBT-70 project. The gun could fire conventional Kinetic Energy (KE) rounds, or launch Anti-Tank Guided MIssiles (ATGMs). The other gun was the 120 mm Delta Gun. This was a Hyper-Velocity Gun that was smooth-bore and fired an Armor-Piercing Fin-Stabilised Discarding-Sabot (APFSDS) round. The gun also used combustible cartridge cases, meaning the entirety of the round would ignite upon firing, much liked the bagged charges used on the 120 mm gun of the British Chieftain.
Another modification that Chrysler designed for the M60 was for the suspension, specifically the torsion bars. A modification by Chrysler allowed the wheels to have an extra 45 percent travel when actuating on their suspension arms.

Despite notable merits to the Chrysler’s ‘K’ tank, the design was not accepted into service. Two mockup turrets were constructed and tested on M60 hulls, but at the time, all spare funds were being spent on equipment for the lingering Vietnam War. As such, all work on the vehicle was dropped.

Chrysler’s other ‘K’ tank from 1968. This time being a possible upgrade of the M60. This is the first version with the MBT-70s XM150 152mm Gun/Launcher. Photo: Presidio Press


Profile of the Chrysler ‘K’ Heavy Tank with a speculative livery of Olive Drab with basic US Markings. Both the color and markings were commonplace at the time. Length and height wise, the ‘K’ wouldn’t have been much larger than the United States then serving tank, the M26 Pershing. At the time, the M26 was considered a Heavy Tank.


A head-on view of the ‘K’ Heavy Tank. This view shows just how wide tank would’ve been. While the ‘K’ was only a maximum of 7.62 cm (3 in) taller and longer than the M26, it was much wider at 3.9 m (12ft 8in), approximately 40cm (16in) wider than the M26. Note also, the 76.2 cm (30 in) wide tracks, and how far the remote rear turrets extend from the hull sides.

Both of these Illustrations were modeled by Mr. C. Ryan and were funded by our Patreon Campaign.

Specifications

Dimensions (L-w-H) 8.72 x 3.9 x 2.6 Meters (28 ft 7.5 in x 12ft 8in x 8ft 8in)
Total weight, battle ready 60 tons
Armor Bow: 18cm (7in), angled at 30-degrees (36cm, 14in, effective)
Sides: 7.62cm (3in), angled 20-degrees (8.1cm, 3.1in, effective)
Turret Face: 18cm (7in)
Turret Sides/Top/Rear: 7.62cm (3in)
Crew 4 (Commander, Driver, Loaders, Gunner)
Propulsion 1,200 hp Chrysler Petrol/Electric engine
Suspensions Torsion bars
Armament Main: 105mm Gun T5E1 Sec: 2 x Browning M2HB 50. cal (12.7mm) MGs in remote turrets, 3 x cal.30 (7.62 mm) Browning MGs. 2 x in fixed mounts on the bow, 1 x coaxial.

Sources

Presentation by Mr. F. W. Slack, 14th May 1946. Original document provided by The Richard Hunnicutt Collection in the at the National Armor and Cavalry Museum Archives. Thanks for this are also extended to the Museum’s Curator, Rob Cogan.
Presidio Press, Firepower: A History of the American Heavy Tank, R. P. Hunicutt
Presidio Press, Patton: A History of the American Main Battle Tank, Vol. 1, R. P. Hunicutt

Categories
Cold War US Heavy Prototypes

120mm Gun Tank T110

U.S.A (1954)
Heavy Tank Concept – Wooden Mockup Built

Improving the Breed

Even while the T43 (M103) was still in development, the U.S.A. was not done with attempts at making better heavy tanks. Development was split into two schools of thought. One based its work on the T43, leading to the T57 and T58 auto loading tanks; and the other started from scratch.

In June 1954, the Detroit Arsenal held its third Question Mark Conference, the goal of which was brainstorming ideas for new heavy tanks. Suggested designs included the TS-2, TS-5, TS-6, and TS-31.

Conditions these proposals had to meet were that a prototype had to be constructed within two years (hence “TS”, for “Tracked vehicle Short Development”), and it had to be able to fit within the confines of the Berne International Clearance Diagram; a code of standardization for rail tunnels established at the international conference at Berne, Switzerland, in 1913. (There is no single Berne National Tunnel, as claimed by Hunnitcutt’s ‘Firepower’; this was merely a building code for rail tunnels)

The TS-2 and TS-5 were both armed with a 105 mm (4.13 in) T210 smoothbore gun; in a turret on the TS-2, and in a fixed casemate on the TS-5.
The TS-6 and TS-31 were armed with the 120 mm (4.72 in) T123E1 gun; again in a turret on the TS-6, and casemate on the TS-31.

Power for the tanks would have been supplied by either a 700 hp Continental AOI-1490-1 engine with an XT-500 transmission (TS-2 and TS-5), or an 810 hp Continental AVI-1790-8 with an XT-500 transmission (TS-6 and TS-31).

In the end, the TS-31 was chosen for further development; it had a gimbal gun mount, and was estimated to weigh 45 tons. Chrysler was assigned to the development of the TS-31, which was given the designation “120mm gun tank T110”; at the same time, the T43 was entering pre-production.

The TS-31/T110 had a driver in the hull, a gunner to the left of the gun, a commander and his machine gun cupola to the right of the gun, and two loaders. It was rear-engined and had six roadwheels on either side. Armor was to be as thick as 9 inches (228.6 mm) on the gun mantlet. Despite the TS-31 concept being chosen as the winner, it still was slightly too big to fit through the Berne Clearance Dimensions. Additional problems were found with the off-center commander’s cupola: the additional metal to support it added to the tank’s weight and increased its size. These flaws led to Chrysler redesigning the tank.

Losing Some Weight

The second draft was an improvement over the original TS-31. It was slightly smaller, becoming shorter and the front becoming flat. The driver was moved into the casemate, to the left of the gun, with the gunner being moved to the right of the gun. Behind the driver and gunner were two loaders and the commander behind them. The commander was placed directly in the middle of the tank, leaving him to sit almost directly atop the engine and with his feet worryingly close to the gun breech. Despite all this, it was still too big to fit through the Berne Clearance Dimensions. Size, in addition to the Detroit Arsenal’s disapproval of the driver’s position, led to a second redesign.

The third draft was sort of a reversion to the original; the driver was moved back to the hull outside of the casemate, and the gunner was moved back to the left of the gun. The commander’s turret was moved slightly forward, so he would no longer have to sit on the engine, but was now forced to sit in a very awkward and cramped position in order to avoid being crushed by the gun’s recoil every time it fired. The casemate reverted to being rounded at the front. The third draft was no smaller in size than the second.

Detroit Fires Back

The Detroit Arsenal replied to Chrysler’s two proposals with the fourth draft of the T110. The casemate was moved to the back, hanging over the rear of the tank. The transmission was moved to the rear as well, joining the engine. In its place up front was a massive fuel tank, nearly encompassing the driver. The power plant (which was now a Continental 700 hp AOI-1490) was pushed to the left to afford the commander a more comfortable (but still probably hot) position on the far rear right. The suspension was changed to a more conventional (for the Americans) type, with smaller road wheels; although the original draft is without them, return rollers would have been necessary.

Hammering out a Design

Chrysler rejected the Detroit Arsenal’s idea to put the casemate on the very back on the tank and kept it in the middle. The driver was moved back inside the casemate, to the right of the gun. You may know this vehicle as the T110E3 or E4, although these designations are completely fictional. Chrysler originally tried to simplify maintenance on this design by allowing the engine to be pulled out, on rails, via a hatch in the rear of the tank. This feature created rigidity issues and the engine was returned to a standard position, now turned lengthwise in the tank. This new engine placement again left the commander stuck between the engine and the gun breech. The gun mantlet, which had been relatively tiny before, was much bigger in this iteration; weighing 2 tons and being 9 inches (228.6 mm) thick. The tank was now short enough to fit through the Berne Tunnel, but it was still too wide.

This version of the T110 was the first to have serious work done on it. A wooden mockup was built and engineering diagrams were drawn up. Gun traverse was 15 degrees to each side, with 20 degrees of gun elevation and 10 degrees of gun depression. Armor was 5 inches (127 mm) at a 60 degree slope from vertical. Secondary weaponry comprised the commander’s .50 cal (12.7 mm) M2 Browning, as well as a .30 cal (7.62 mm) paired with the main gun.

Artist's interpretation of design five
Artist’s interpretation of design five

The original TS-31/T110
Small scale model of design five

At some point, Chrysler realized that there was no need to stick with a casemate design, as a turret could be accounted for within the weight requirements for the tank. In its sixth iteration, the T110 was completely changed, becoming a far more conventional tank. The driver was moved to the middle of the hull, under the gun barrel. The crew was reduced to four instead of five men by dropping a loader. To ease the life of the remaining loader, a gun rammer was fitted. The gunner was on the left of the turret, with the commander above and behind him, and the loader on the right. This, the last version of the T110, shared the 85 inch (2.16 m) turret ring with the M103. Engineering diagrams and a small-size mockup were made, but by this time the T43E2 had been built and showed promise. The success of the M103, as well as changing ideas in terms of tank design, were the doom of the T110, and the project was canceled.

Artist's interpretation of design six
Artist’s interpretation of design six

The original TS-31/T110
Small scale model of design six

Even the definitive version of the T110 failed its main goal, as it was still too big to fit through the Berne Clearance Dimensions.

The original TS-31/T110
The original TS-31/T110

Chrysler's first revised T110
Chrysler’s first revised T110

Chrysler's second revised T110
Chrysler’s second revised T110

The Detroit Arsenal's T110 counter-proposal
The Detroit Arsenal’s T110 counter-proposal

The fifth T110 design -Chrysler
The fifth T110 design -Chrysler

The fifth T110 design -Chrysler
The original TS-31/T110
Schematics of the fifth T110 design

The sixth T110 design -Chrysler
The sixth T110 design -Chrysler

The original TS-31/T110
Schematic of the sixth T110 design

T110, Draft Six specifications

Total weight, battle ready Probably around 50 tons
Crew 4 (driver, gunner, commander, loader)
Propulsion Continental 700hp AOI-1490
Suspension Torsion Bar
Armament 120 mm (4.72 in) T123E1 rifled cannon
Total production A few wooden mockups

Sources

Presidio Press, Firepower: A History of the American Heavy Tank, R.P. Hunnicutt.
Originally published on November 13, 2016.


The fifth T110 design submitted by Chrysler. The 120 mm cannon is mounted in a fixed superstructure, with a machine gun armed commander’s cupola on the roof. Illustration by Jaroslaw “Jarja” Janas.

Categories
Cold War US Heavy Prototypes

155mm Gun Tank T58

U.S.A. (1952)
Heavy Tank Prototype – 2 Turrets Built

In the early 1950s, the American military’s quest for a powerful new heavy tank was well underway. The T28, T29, T30, T32, and T34 projects had all ceased in favor of the 120mm Gun Tank T43, which eventually became America’s last heavy tank, the M103.
While still in development as the T43, however, there were parallel projects competing for the role of America’s next heavy tank. One of these projects was the 120mm Gun Tank T57. It used the same hull as the T43, but incorporated new technologies for the turret. The turret was of the oscillating kind, but it was also outfitted with an autoloading mechanism.
In the Army Development Guide of December 1950, both the T43 and T57 were expected to more than meet the requirements of the military and be a worthy adversary of Soviet armor such as the infamous IS-3. However, in the Tripartite Conference of Armor and Bridging of October in 1951, it was recommended that a 155mm gun armed tank be developed instead.

A mockup of the T58 Heavy Tank. Photo: Presidio Press

Development

A list of recommended characteristics for this new heavy tank was outlined in a paper on the 18th of January 1952. Such recommendations included a gun that exclusively fired HEAT (High-Explosive Anti-Tank) or HEP (High-Explosive, Plastic. Otherwise known as HESH – High-Explosive Squash Head) rounds. This paper also recommended the construction of two prototype turrets complete with autoloaders and 155mm guns for installation on T43E1 chassis. The resulting vehicle received the designation of 155mm Gun Tank T58.
On the 10th of April 1952, a contract was drawn up with United Shoe Machinery Corporation of Beverly, Massachusetts for the design, development and manufacture of the two pilot turrets.

Hull

The hull that was used for the project was the same as that of the 120mm Gun Tank T43, which would later be serialized as the M103, America’s last heavy tank. Armor on the hull was the same. The cast ‘beak’ was 3.9 – 5.1 in (100 to 130 mm) thick.
An 810hp Continental AV1790 12-cylinder air-cooled gasoline engine propelled this chassis to a speed of around 21 mph (34 km/h). The tank’s weight was supported on seven road wheels attached to torsion bar suspension. The drive sprocket was at the rear while the idler wheel was at the front. The idler wheel was of the compensating type, meaning it was attached to the closest roadwheel by an actuating arm. When the roadwheel reacts to terrain the idler is pushed out or pulled in, keeping constant track tension. The return of the track was supported by six rollers.

Turret

The T58’s turret was one of the largest oscillating turrets ever designed, at approximately ¾ the length of the hull. Changes had to be made to the T43/M103 hull to accommodate the new large turret. When initially tested on one of the hulls, the turret bustle would collide with the mufflers of the main engine and auxiliary generator located on the engine deck. To fix this issue, the mufflers were relocated 20-inches (51cm) to the rear. A new travel lock was added to the deck to accommodate the larger gun.
This turret had similarities to the T69 medium tank prototype, in that its roof had multiples ways of ingress and egress. The turret roof was constructed from two removable plates. The rear plate was bolted in place, while the front section, like the T69, was hinged and could be opened outward by use of a hydraulic piston. The large opening made it easier to exit the turret in an emergency. In the open position, this opened section also provided a shield for the crew while evacuating. These sections were designed to be easily removed to permit installation of the autoloader mechanism and other components.
A ventilator was placed at the rear-right of the turret atop the bustle to vent gases and smoke produced when the gun is fired.

Line drawing of a face-on view of the T58. Note the size of the turret. Photo: Presidio Press

Links, Resources & Further Reading

Presido Press, Firepower: A History of the American Heavy Tank, R. P. Hunnicutt
An official US Government report dated April 1954. READ HERE
On History of War


A cut-away view of the inside of the T58’s turret. Photo: Presidio Press

Armament

Originally, it was planned to utilize the 155mm Gun T80. This proved unnecessary as the chosen ammunition for the gun was of the chemical type and did not require the high-velocity granted by the T80. Designers instead opted for a lighter weight version of the lower velocity 155mm Gun T7, the gun developed for the Heavy Tank T30. Firing HEAT through this gun, the maximum armor that could be penetrated (angled at 0 degrees) was 16 inches (406mm).
This modified version of the T7 was originally designated as the 155mm Gun Howitzer T7E2. It was later changed, however, to ‘155mm Gun Howitzer T180’. There was no actual change to the gun, just a change in nomenclature. The T180 differed greatly from the original T7 though. The breech block was changed from a horizontal to a vertically sliding type. A bore evacuator (fume extractor) was added towards the end of the gun, and a T-shaped blast deflector installed on the muzzle. The gun tube wall was thickened and the chamber lengthened about an inch (~25mm) to accommodate the plastic closing plugs used on the cartridge cases of the two-part ammunition.
Unlike the T57 that had a rigidly mounted gun, the T58 was outfitted with a four-cylinder hydro spring recoil system in a mount designated the T170. There were 2 springs to each side of the breach. To save space and remove the need of extending the length of the turret, the recoil of the gun was limited at 12 to 14 inches.
Secondary armament consisted of a coaxial .30 Cal (7.62mm) Browning machine gun, and a .50 cal (12.7mm) Browning heavy machine gun mounted atop the commander’s cupola. The oscillating turret provided an elevation of 15 degrees, with a depression of 8 degrees. The original specifications included a second coaxial machine gun, but this was not included.
The main gun was aimed via periscopic sights. There was one lens on each side of the turret, known as ‘frog’s eyes’. These types of sights were used on many American tanks from the early 1950s onwards, including such tanks as the T69, M48 and M60.
The armor on both the collar and upper part the turret was extremely thick, but exact measurements are unfortunately unknown.

Autoloader

The 155mm gun was fed by an autoloading mechanism located in the turret bustle. It was not too dissimilar to the one used on the T69 medium tank prototype, consisting of a 6-round cylinder magazine with an incorporated rammer. On the T69, it actuated up and down during the loading sequence. On the T58, due to the size and sheer weight of a fully loaded magazine, the cylinder was fixed in place.

Two diagrams looking at the front and back of the auto-loading mechanism. Photo: Presidio Press
The loading sequence was thus: The loader used an internal, electrically powered hoist attached to the turret roof to remove one of the 95 pound (45kg) shells from the ready rack and insert it into the loading tray of the cylinder. The round was then slid into an empty cylinder chamber. The loader then selected the requested ammo type by manually rotating the cylinder with a hand crank. The separately-loading ammunition (projectile then charge) was rammed into the breach as one unit. After firing, the empty propellant cartridge was ejected back into the cylinder, where it was removed by the loader before the sequence began anew.

Crew

The crew consisted of a Commander, Gunner and Loader located in the turret and Driver in the front of the hull. The Gunner was located at the front right of the turret, the Commander sat behind him under a vision-cupola. The Loader was positioned on the left of the turret under his own hatch.

Fate

Work on two pilot turrets continued into 1956 despite numerous design changes during production and delays in obtaining and producing various parts required for assembly. By this time, however, trends had shifted, and a tank such as the T58 was no longer thought a necessary to the military.
The T58 project, along with the T57 and many other projects, was canceled on the 17th of January 1957. Following this outcome, both pilot turrets were scrapped. All that survives today are a few photos and government reports.

An article by Mark Nash

Specifications

Dimensions (L-w-H) 37.14 x 12.34 x 9.45 ft (11.32(oa) x 3.76 x 2.88 m)
Total weight, battle ready Around 62.5 tons (125 000 lbs)
Crew 4 (Commander, Driver, Loaders, Gunner)
Propulsion Continental AV-1790-2 V12, AC Twin-turbo diesel 810 hp.
Transmission General Motors CD-850-3, 2-Fw/1-Rv speed GB
Maximum speed 21 mph (34 km/h) on road
Suspensions Torsion bars
Armament Main: 155mm Gun Howitzer T180 Sec: 1 Browning M2HB 50. cal (12.7mm), 1 cal.30 (7.62 mm) Browning M1919A4
Production 2


Illustration of the 155mm Gun Tank T58 by Tank Encyclopedia’s own David Bocquelet.